1. Field of the Invention
The present invention relates generally to expandable tubular structures capable of insertion into small spaces in living bodies and, more particularly, concerns a stent structure having a geometry which is capable of substantial and repeated flexing at points along its length without mechanical failures and with no substantial changes in its geometry.
2. Description of the Related Art
A stent is a tubular structure that, in a radially compressed or crimped state, may be inserted into a confined space in a living body, such as a duct, an artery or other vessel. After insertion, the stent may be expanded radially to enlarge the space in which it is located. Stents are typically characterized as balloon-expanding (BX) or self-expanding (SX). A balloon-expanding stent requires a balloon, which is usually part of a delivery system, to expand the stent from within and to dilate the vessel. A self expanding stent is designed, through choice of material, geometry, or manufacturing techniques, to expand from the crimped state to an expanded state once it is released into the intended vessel. In certain situations higher forces than the expanding force of the self expanding stent are required to dilate a diseased vessel. In this case, a balloon or similar device might be employed to aid the expansion of a self expanding stent.
Stents are typically used in the treatment of vascular and non-vascular diseases. For instance, a crimped stent may be inserted into a clogged artery and then expanded to restore blood flow in the artery. Prior to release, the stent would typically be retained in its crimped state within a catheter and the like. Upon completion of the procedure, the stent is left inside the patient's artery in its expanded state. The health, and sometimes the life, of the patient depend upon the stent's ability to remain in its expanded state.
Many conventional stents are flexible in their crimped state in order to facilitate the delivery of the stent, for example within an artery. Few are flexible after being deployed and expanded. Yet, after deployment, in certain applications, a stent may be subjected to substantial flexing or bending, axial compressions and repeated displacements at points along its length, for example, when stenting the superficial femoral artery. This can produce severe strain and fatigue, resulting in failure of the stent.
A similar problem exists with respect to stent-like structures. An example would be a stent-like structure used with other components in a catheter-based valve delivery system. Such a stent-like structure holds a valve which is placed in a vessel.